Some patients develop conditions that can be corrected with implantable medical devices such as mechanical and bioprosthetic heart valves, coronary stents, stent grafts, abdominal aortic aneurysm (AAA) grafts and other devices. Conditions that affect blood flow through the vessels of the body, for example, may be treated with vascular grafts, in which a surgeon applies the graft to supplant the damaged vascular tissue. Coronary artery disease, peripheral vascular disease and venipuncture for treatment of end stage renal disease are examples of conditions in which vascular flow is affected, and which can be addressed with surgical grafts.
Vascular grafts may be autologous, i.e., the graft may be taken from the patient for transplantation at another site. In some cases, however, an autologous graft may not be feasible, and a synthetic vascular graft may be employed instead. A synthetic vascular graft is a tube-shaped prosthesis made of a biocompatible material such as expanded polytetrafluoroethylene (ePTFE). The synthetic vascular graft includes a lumen through which blood flows.
In a vessel, the intima is the layer closest to the lumen where blood flows. It is made up mainly of a monolayer of endothelial cells attached to a basement membrane and matrix molecules. The endothelial cells are specialized cells that line the lumen of blood vessels, and play several roles. Endothelial cells secrete vasoactive substances, for example, and secrete substances that stimulate new vessel growth and promote or inhibit contraction and sometimes proliferation of smooth muscle cells in vessel walls in response to hemodynamic demands. Endothelial cells are also influential in formation and dissolution of thrombus, which is a precipitate of blood components that can restrict blood flow through the vessel lumen.
In humans, implanted vascular grafts typically heal by formation of an acellular psuedo-intima without large-scale outgrowth of the native endothelial cell lining at the point of anastomosis. It has been discovered that it is highly beneficial for a synthetic vascular graft to include a layer of endothelial cells in the lumen, to prevent thrombosis and to suppress abnormal smooth muscle cell proliferation that could lead to stenosis or narrowing of the vessel. To promote the formation of a homogeneous, dense and confluent layer of endothelial cells inside the synthetic vascular graft, techniques have been developed for “endothelial cell seeding” of vascular grafts. In general, this “seeding” or deposition of cells involves harvesting autologous endothelial cells and transplanting the harvested cells to the lumen of the synthetic vascular graft.